Process for the production of unsymmetric and/or symmetric dialkyl carbonates and diols

Abstract

A process for the production of a dialkyl carbonate and a diol, such as dimethyl carbonate and ethylene glycol, by reacting a feed containing a cyclic carbonate, a hydroxy alkyl carbonate and an aliphatic monohydric alcohol in the presence of a transesterification catalyst is described. In another aspect, a process is described which is particularly useful for producing unsymmetric dialkyl carbonates, such as ethyl methyl carbonate.

1. A process for the production of a dialkyl carbonate and a diol from an alkylene oxide, carbon dioxide and an aliphatic monohydric alcohol comprising:
 (a) reacting an alkylene oxide with carbon dioxide in the presence of a carbonation catalyst at a temperature in the range of about 50 to 250° C. and at a pressure of at least about 1379 kPa (200 psi) to provide a crude cyclic carbonate stream comprising a cyclic carbonate and carbonation catalyst; and 
 (b) reacting said cyclic carbonate and a hydroxy alkyl carbonate with said aliphatic monohydric alcohol in the presence of a transesterification catalyst, thereby producing a crude product stream comprising said dialkyl carbonate, said diol and said hydroxy alkyl carbonate; and 
 (c) separating said hydroxy alkyl carbonate from said crude product stream and recycling said hydroxy alkyl carbonate to step (b). 
 
     
     
       2. A process according to  claim 1 , wherein said dialkyl carbonate comprises an unsymmetric dialkyl carbonate. 
     
     
       3. A process according to  claim 1 , wherein reaction step (b) occurs at a temperature in the range of from about 20 to 300° C. and a pressure of from about 14 to 4000 psig. 
     
     
       4. A process according to  claim 1 , wherein reaction step (b) occurs at a temperature of at least about 250° C. 
     
     
       5. The process according to  claim 1 , wherein the molar ratio of said hydroxy alkyl carbonate to said cyclic carbonate is in the range between about 0.01:1,000 to about 0.01:100. 
     
     
       6. The process according to  claim 5 , wherein said molar ratio of hydroxy alkyl carbonate to said cyclic carbonate is about 0.1:10. 
     
     
       7. The process according to  claim 1 , wherein said aliphatic monohydric alcohol and said hydroxy alkyl carbonate have different alkyl groups. 
     
     
       8. The process according to  claim 1 , wherein the molar ratio of said aliphatic monohydric alcohol to said cyclic carbonate equivalents is in the range between about 2:1 to about 6:1. 
     
     
       9. The process according to  claim 8 , wherein the molar ratio of said aliphatic monohydric alcohol to said cyclic carbonate equivalents is in the range between about 3:1 to about 4:1. 
     
     
       10. The process according to  claim 3 , wherein said reaction step (b) is conducted at a temperature between about 80 to 200° C. and a pressure between about 700 Kpa (100 psi) to about 2000 Kpa (300 psi). 
     
     
       11. The process according to  claim 10 , wherein the conversion of said ethylene carbonate to said dimethyl carbonate is between about 30 to about 70%. 
     
     
       12. The process according to  claim 11 , wherein the conversion of said ethylene carbonate to said dimethyl carbonate is between about 40 to 65%. 
     
     
       13. The process according to  claim 1 , wherein reaction step (b) occurs at a temperature of between about 50 to about 250° C. and a pressure of between about atmospheric to about 14,000 Kpa (2000 psi). 
     
     
       14. The process according to  claim 13 , wherein said reaction step (b) occurs at a temperature of between about 75 to about 140° C. and a pressure of between about 140 Kpa (20 psi) to about 2,000 Kpa (300 psi). 
     
     
       15. A process according to  claim 1 , wherein R 3  and R 4  are the same and said dialkyl carbonate is symmetric. 
     
     
       16. A process according to  claim 1 , wherein R 3  and R 4  are different and said dialkyl carbonate is unsymmetric.